The present invention relates to a sheet feeding apparatus, and more particularly to a sheet feeding apparatus to be used in an automatic sheet feeder.
An automatic sheet feeder is widely used in a printer, a fax machine and a scanner. One of the most important components of the automatic sheet feeder is a cantilever sheet feeding apparatus. The typical structure of the cantilever sheet feeding apparatus used in an automatic sheet feeder includes not only a motor for providing power to feed a sheet but also an expensive magnetic valve or another motor for controlling the motion of a cantilever. Such structure has disadvantages of high cost and a complex assembly. Thus, the structure of the sheet feeding apparatus needs to be improved to overcome the above problem.
It is therefore an object of the present invention to propose a sheet feeding apparatus adapted to be used in an automatic sheet feeder which has a motor rotatable in a first direction and a second direction. The sheet feeding apparatus includes a first transmission device driven by the motor for generating a driving force, a second transmission device driven by the first transmission device when the driving force for driving the second transmission device is larger than a threshold value, and a third transmission device moving between an initial position and a sheet feeding position and driven by the second transmission device to rotate in the first direction for moving from the initial position to the sheet feeding position where the third transmission device is in contact with a sheet while the motor rotates in the first direction and the driving force for driving the second transmission device is smaller than the threshold value so that when the driving force for driving the second transmission device becomes larger than the threshold value, the third transmission device feeds the sheet.
According to an aspect of the present invention, the third transmission device will rotate in the second direction to back to the initial position when the driving force for driving the second transmission device further becomes smaller than the threshold value and the motor rotates in the second direction.
Preferably, the first transmission device includes a first gear driven by the motor, a transmission shaft connected through the first gear, an one way bearing coupled with the transmission shaft, a separation roller coupled with the one way bearing and rotating therewith, and a second gear coupled with the transmission shaft to drive the second transmission device.
Preferably, the one way bearing and the separation roller rotate in the first direction on the transmission shaft while the motor rotates in the first direction and are free to rotate in the first direction while the motor rotates in the second direction.
Certainly, the sheet feeding apparatus can further include a cantilever coupled with the transmission shaft and connected to the second transmission device and the third transmission device.
Preferably, the second transmission device includes a connecting shaft fixed to the cantilever, a third gear coupled with the connecting shaft and meshed with the second gear of first transmission device, a torque limiting module mounted on the connecting shaft and between the connecting shaft and the third gear.
Preferably, the third transmission device includes a sheet feeding shaft coupled with the cantilever, a fourth gear coupled to the sheet feeding shaft and meshed with the third gear, and a sheet feeding roller connected to the fourth gear and also coupled with the sheet feeding shaft, wherein the cantilever is driven by the motor to rotate in the first direction on the transmission shaft to move the sheet feeding roller from the initial position to the sheet feeding position where the sheet feeding roller is in contact with the sheet while the driving force for driving the third gear is smaller than the threshold value and the motor rotates in the first direction. The fourth gear and the sheet feeding roller is driven by the third gear to feed the sheet while a reaction force of the sheet feeding roller in contact with the sheet is generated to make the driving force for driving the third gear larger than the threshold value and the third gear starts to rotate, and then the cantilever driven by motor rotating in the second direction rotates inversely on the transmission shaft and is moved from the sheet feeding position to the initial position while the motor rotates in the second direction and the driving force for driving the third gear is smaller than the threshold value.